The present invention relates, in general, to containers for beverages and, more particularly, to plastic closures for wide-mouthed plastic cans particularly suitable for packaging liquids such as carbonated beverages.
Metal cans have long been in use for packaging soft drinks and like carbonated beverages, and have satisfactorily met the needs of the beverage industry. However, the introduction of so-called "plastic cans" is being considered by the soft drink industry for a variety of reasons, including the fact that such containers enjoy some cost advantage over metal cans. One of the problems faced in the production of plastic cans is the difficulty encountered in securing a suitable closure that is easy to make and easy to install, and which will be secure enough to withstand the internal pressures generated by carbonated beverages when sealed in containers.
A "plastic can" may take a variety of shapes, and may be of any desired size, but, generally, is a cylindrical container capable of holding about 12 fluid ounces, and is formed of a plastic material such as polypropylene, polyvinyl chloride (PVC), polyethylene terephthalate (PET), or the like, with PET being the preferred material. Such a material has the strength required to withstand the pressures, of up to about 150 psi, which can be generated by a carbonated beverage, limits the permeation or leakage of carbon dioxide so that beverages will have a long shelf life, and does not require the internal coating which is needed by a metal container to avoid adversely affecting the taste of the contents. Such a plastic container is transparent, and has the consequent marketing advantage of enabling customers to see what they are buying. Further, such a container has good thermal insulating qualities, so that the container does not feel as cold to the touch as does a metal container when the contents are chilled. A container of this type is closed at the bottom by a concave, spherical bottom wall to provide the required strength characteristics, and has a wide mouth at the top, preferably extending across substantially the entire diameter of the container, which must be closed after the container is filled. The present invention provides a plastic closure for such containers.
It has been proposed to close the mouth of a plastic can with a metal lid, preferably aluminum, which is similar to the lids commonly used on metal beverage cans. Such lids have been applied to the upper edges of the plastic cans by a crimping process, and although this process has been found to be workable, it is not without problems. First, the crimping of such lids onto the container involves a multi-step process which includes the application of a sealant material between the lid and the container, the application of the lid, and a crimping operation. These multiple manufacturing steps are expensive and time-consuming, and thus the use of a metal lid is not entirely satisfactory. Furthermore, the combination of a metal lid with a plastic closure is deemed by many to be aesthetically unappealing, and thus does not have the marketability that is anticipated for an all-plastic container and lid combination. In addition, a metal lid on a plastic can significantly increases the cost of recycling the container, for the lid must be removed from the can so that the two materials can be separately handled in the recycling process. Since the recycling of the materials has become an important factor in the manufacturing and marketing of containers, provision of a container and closure formed of a single material is highly desirable. However, no completely satisfactory plastic closure has yet been devised for plastic cans which would provide easy installation, secure sealing of the container, and the ability to withstand high pressures for a long shelf life. In particular, no previous design has been found that will allow a snap-on fit between a plastic can and its plastic lid, which will not require additional sealing materials between the can and the lid, and which will allow the use of the same materials for both components for facilitating recycling of the materials.
Thus, there is a significant need for a plastic lid, or closure, for a wide-mouthed plastic beverage can which will overcome the various problems encountered with the use of metal lids on plastic cans, as outlined above, including allowing the entire container to be recycled without the need for a prior separation of the two components. A plastic lid for a plastic can would reduce the cost of such containers, particularly if a simplified procedure for securing the lid to the can could be found which would eliminate the steps of crimping and sealing which are now used. Further, such a lid would complement the appearance of the plastic container, and would, therefore, result in a more marketable product.